Magnesium base alloy



Patented Nov. 24. 1942 7 2,302,968 MAGNESIUM Bass ALLOY John C.McDonald, Midland, Mich., assignor to The Dow Chemical Company, Midland,Mich, a corporation of Michigan No Drawing. Application June 15, 1940,Serial No. 340,786

3 Claims.

This invention relates to magnesium base alloys. It more particularlyconcerns an. alloy of this nature having desirable physical properties,such as excellent yield'and tensile strengths, coupled with goodformability.

Magnesiumv alloys are being extensively employed in the variousstructural and mechanical arts where the use of a light weight metal ishighly advantageous, such asfor use in making castings, forgings, andthe like. However, the use of magnesium alloys in rolled form to makesheet metal articles requiring forming operations, such as bending,drawing, and the like, has not progressed as rapidly due to the factthat in.

general alloys of good formability, permitting relatively sharp bends tobe made without the article developing external cracks, usually lackdesirable strength characteristics.

It is, accordingly, the principal object of the invention to provide amagnesium base alloy having high yield and tensile strengths andpossessing suflicient ductility or formability to be sharply bent, drawnor otherwise shaped.

Other objects and advantages of the invention will be apparent as thedescription of the invention proceeds.

My invention resides in the discovery that a magnesium basealloy'composed of from 1 to 20 per cent of thallium and from 0.01 to lper cent of cerium, the balance being magnesium, possesses theaforementioned properties. The term' "cerium used'herein and in theappended claims .is intended to include not only elemental cerium,

and contains, besides cerium, varying-amounts of other rare earthmetals. As an example, the fol- I lowingvis considered an averagecomposition of Misch-metal as commercially obtainable: cerium 40-50 percent, lanthanum 30-40 per cent, dysprosium and samarium and other rareearth metals 10 per cent, and iron 5 per cent. The term "magnesium usedherein and in the apinthe commercially pure nietal, such as traces ofiron, copper, nickel, and silicon.

While the properties of good formability or ductility associated withexcellent tensile and yield strengths are manifest over the entire rangeof the composition indicated, I have found that the most satisfactory.combination of properties is obtained when the alloy contains from about3 to 12 per cent of thallium and from about 0.1 to 0.3 per cent ofcerium. The specific proportion of each alloying metal a'ndthe totalamount of alloying metals to be added to the new alloy depends upon theuse for which the alloy is intended. For example, when an alloy havingexceptionally. high ductility or formability coupled with good yield andtensile strengths is desired, the alloy should preferably be made upcontaining from about 2 to 8 per cent of thallium and from about-0.1 to0.3 per cent of cerium. In those instances when it is desirable to forman alloy. of exceptionally high yield and tensile strengths coupled withsatisfactory ductility, the

thallium content of the alloy should be increased to about 12 to 20 percent. I The following table lists some of the properties of rolled sheetmade from my new alloy and compares these properties with those ofrolled sheet made from related alloys. A comparison of the propertiesillustrates the improvement in strength characteristics of my new alloyover those of the closely related alloys. In the table, the per centelongation is to be regarded as a measure of the ductility orformability of the specimen.

Table Nominal composi- 32: 3' 9%: Annealed Cold rolled maindor) Tl 2, 8Yield Tensile Yield Tensile 2 inches strength strength strength strengthPer cent Lba/sq. in. Lba. sq. in. Lbs. in. Lbs. in. 6. 0 10 21, 000 33{000 32{ 0 00 0.18 16 1 000 32,000 24,000 32,000 5. 0 0. 18 21 23, 00036, 000 30, 000 38, 000 10.0 l6 m000' 33,000 29,000 33,000 0.16 1616,000 32,000 24,000 3 000 10.0 0.16 17 21,)0 36,000 36,000 39,011

pended claims, is intended to include magnesium containing the ordinaryimpurities that are found.

The properties listed in the above table under the section headed by theterm "annealed were obtained by first rolling the alloys in atemperature rangeof from 550600 F. and thereafter annealing them atvarious'temperatures in the temperature range from 400 to 800 F. Theproperties selected for the table were those of the annealed specimenswhich exhibited the maximum elongation. Properties set forth in thetable under the section headed "cold rolled were obtained by subjectingspecimens of the alloy which had first been hot rolled at a temperatureof from 550 to 600 F. to additional'rolling in the cold state. Theproperties selected for the table were those of the cold rolledspecimens which showed the greatest tensile and yield strengths whilehaving at least a 1 per .cent elongation in 2 inches.

While' the new alloy is most useful inthe wrought form, such as sheets,due to its forma- A comparison of the properties listed in the tableshows that the combined properties of my new alloy are superior to thoseof the related alloys having similar percentages of alloyingingredients. For example, it will be noted that the alloys containinglower percentages of alloying ingredients have excellent elongationcoupled with markedly superior strength properties in bilitycharacteristics, it may also-be suitably used in making castings,forgings, extruded forms, and the like. A

My new alloy may be prepared by any of the methods employed for meltingand alloying metals with magnesium, such as by adding the respectivealloying metals singly or jointly to a bath of molten magnesium which ispreferably protected from oxidation by a suitable flux.

The cerium may be added to the alloy as such or in the form ofMisch-metal. Magnesiumcerium alloys are commonly made up by employingMisch-metal as asource of cerium. An

amount of Misch-metal is employed such as will give the desiredpercentage of elemental cerium in the'alloy. It is sometimes desirableto add more than the theoretical amount of Misch-meta1, since thealloying efliciency is not always per cent and some loss maybe incurred.

I claim:

1. A magnesium base alloy containing from 1 to 20 per cent of thalliumand from 0.01 to 1 per cent or cerium, the balance being magnesium.

2.- A magnesium base alloy containing from 2 to 8 per cent of thalliumand from 0.1 to 0.3 per cent of ceriuin, the balance being magnesium.

3. A magnesium base alloy containing from 12 to 20 per cent of thalliumand from 0.1 to 0.3 per cent of cerium, the balance being magnesium.

JOHN c. MCDONALD.

